EQ3 goto mount gears slipping

[LiveC]

Hi,

I have had an eq3 goto mount for a little over a year now.  I use it with a SkyWatcher 127 scope, and find that the gears of the motor slip with grinding noise when the mount is skewing resulting in the scope pointing at the incorrect position.  The scope is balanced and polar aligned.

The clutches are tight.  After 11 months of struggling, never successfully completing a star alignment, and assuming I was doing something wrong, I contacted the store that sold me and they sent it back for repair.  Two months later it was returned but failed again the first time of use.  A colleague who is an keen astronomer had a look and it improved matters but didn't entirely resolve the problem.   

He recommends buying a better mount.  Before I cut my losses and invest, has anyone else encountered similar problems?

Thank you in advance

Clive

[Kropster]

My EQ3-2 goto was making loud clicking noises...... you could feel the RA worm drive shaft jumping.

I think the worm gear was binding, or skipping some how.

I adjusted the gear meshing using the allen bolts that hold it in place.

I think two adjust in and out and the other two clamp it in place.. not really sure, but it fixed the problem.

Perhaps your worm gear is not engaging enough with the RA drive gear?

[Avocette]

Hi Clive and welcome to SGL. Shame that you've had this problem for so long and that you lost two months scope use for no improvement! There are a number of threads on SGL which have dealt with similar issues, and diagnosing the problem may need a bit of trial and error.

Firstly, can you isolate the problem to one axis or the other or is it happening on both axes? Do you hear a mechanical noise when 'the gears slip'?

If the problem is mechanical, then as Kropster suggests the worm gear may not be engaged properly with the mount gear. This is fully adjustable, and normally would be something you would want to check to minimise backlash which would affect your pointing accuracy. But if the gears are slipping, then this adjustment would be so way out that you should have masses of backlash. You can test this by seeing how far you can turn the worm gears before the mount actually moves. When you are looking through the scope at say a bright star in the centre of the field of view, does the mount begin to move equally quickly when you press the North/South or East /West buttons or is there a (large) time lag is one or other direction while the slack is taken up? Equally, when you look through the eyepiece can you move the scope mechanically by hand against the fixed position mount by a large margin (so that the star goes out of view in a 25mm eyepiece)?

If none of this applies, then there may be an electrical problem. This may manifest as an inconsistent sound or rhythm during slewing. Try slewing on both axes independently at different rates (set rate from 0 to 9) and listen for any jerkiness in the resulting sounds. Each slewing speed has a characteristic tone and throbbing rhythm but you get used to this and it doesn't suddenly vary during a long slew.

Final question - did the store you bought it from understand what the problem was and accept that there was a problem and did they claim it had been repaired or was 'no fault found'?

[LiveC]

Thank you for your replies.  

As Kropster reported there is clicking noise that does sound like the teeth of the gears brushing each other but not fully engaging.  This doesn't happen constantly and is only with one axis.  The motors sound fine with the characteristic whine and the smooth transition of the mount until such time as as the 'slipping' occurs.

Using the directional keys operates the motors successfully and again if not 'slipping' moves the mount correctly.  When my colleague looked at this for me he did reseat the motor using the Allen keys and the first time I used it afterwards I was overjoyed that the mount skewed during the alignment process, at speed, successfully.  Having centered it on Jupiter with the low ticking of the motor tracking it did 'jump' after a few minutes.

I will reseat the motor assembly and give it another whirl.

On the subject of the dealer who sold it me, I and not impressed.  From what my coleagues said supported by you guys I believe this is a gear meshing problem rather than a motor failure.  I therefore doubt it was ever returned to the factory.  They assured me it was fully tested, it transpired that these tests where conducted with no scope or counterweights attached, hardly a representative field test.

Thank you again, and I will let you know how I get on 

[LiveC]

An update for you.  I spent the afternoon stripping down the Dec axis of the mount following the excellent step by step instructions posted by Badgers.

The first observation was that the retaining bolt was so tight that even using a socket with a ratchet it took some moving.  I stripped it down degreased, re-greased and reassembled as per the instructions being very careful not to over tighten anything.

The resulted were visibly apparent, the dec axis of the mount now rotated with the weight of the scope the moment the clutch was disengaged, and now the motor has a higher pitched whine clearly no longer struggling.

It has been tested through 360 degrees at room temperature with no problems.  Only one test remain when its at ambient temperature outside, but I am hopeful.

Thanks for your assistance I wouldn't have pursued this course of action without your information.

Clive